UNUSUALLY LOCATED OSTEOID OSTEOMAS

The files of 12 patients (aged 12-33 years) with an equal number of su rgically proven osteoid osteomas (OOs) were reviewed in attempt to fin d a diagnostic algorithm in cases of unusually located OOs. Plain radi ography (PR) and thin collimation computed tomography (CT) had been pe rformed in all patients, while bone scintigraphy (BS) had been perform ed in eight and magnetic resonance imaging (MRI) in two. The OOs were located at juxta- or intra-articular sites, except for one located at the left neck of the L(4) vertebra. The diagnosis based on the MRI exa minations was synovitis. BS showed increased accumulation of the radio isotope at the site of the lesions, without the 'double density' sign. PR showed the nidus of 00 in only six patients, whereas CT located th e nidus in all patients. In conclusion, we believe that when an 00 is clinically suspected at an unusual location, CT should be performed in all cases, even when a lesion is depicted by PR and BS, because CT wi ll not only locate the nidus but will also provide a precise anatomy o f the area around the nidus and help in therapeutic decision making an d surgical planning. MRI can be misleading and must not be used in the initial assessment of a possible osteoid osteoma.